Various uses for cryogenic systems are known. Such uses include providing oxygen supplementation for persons having restricted breathing and providing pneumatic power for small hand tools. Examples of such prior systems are disclosed in U.S. Pat. Nos. 4,149,388; 4,211,086; and 4,838,034.
Cryogenic systems have also long been utilized in the storage and transporting of specimens including human and animal body fluids such as animal semen. Such systems commonly employ a cryogenic dewar to store and/or transport the specimens. Shown in FIG. 1 is such a conventional system comprising a cryogenic dewar that typically includes an inner vessel and an outer container, each having a central opening at their tops, a neck portion providing an air tight connection between the openings of the inner vessel and the outer casing at their tops, thereby forming an evacuable space therebetween, and one or more sample or specimen holders, each provided with an elongated support with a hook at its distal end to engage the top of the dewar. The sample holders are typically immersed in a bath of liquid cryogen, commonly nitrogen, maintained in the inner vessel. The bottom of the inner vessel is provided with means, such as a spider, to maintain the spacing of the specimen holders within the inner vessel to avoid their mutual interference upon insertion and removal. The central opening of the dewar is typically closed or fitted with a foam plug.
The existing cryogenic systems have, however, not been entirely satisfactory. The sample holders have been difficult to identify and difficult to remove from the dewar without interference with other sample holders and the interior surfaces of the dewar itself.